Patients undergoing LAR for rectum cancer is subjected to peritoneal microdialyses during the postoperative period until the 7. postoperative day. Samples are collected every 4-hour. Samples will be analyzed continuously but the results will not be included in the clinical evaluation of the patient. Before removing the microdialysis catheter a CT whit rectal enema is preformed. Every day the patient will be evaluated whit a standardised clinical scoring system with attention at anastomotic leakage.